1. Field of the Invention
This invention is generally directed to flow control devices for use in water wells and particularly to a downhole flow controller for use in recharge, injection and aquifer storage recovery wells wherein the flow controller continuously regulates the flow of water during both periods of water production and well recharging. During well recharging, the recharge water in the pump column of the well is controlled to prevent air from being entrained or trapped in the fluid flow into the aquifer which air entrainment can adversely effect the recharge operations by blocking the flow of water into the aquifer. In addition, the downhole flow controller automatically adjusts so that sufficient intake flow may be established therethrough during pumping or well production operations.
2. History of the Invention
Many communities have, and others are realizing the need for, a major investment in water supply, treatment and distribution facilities. Further, due to variability in both water supply and demand, it is necessary that adequate reserve capacity of these facilities be continuously maintained in anticipation of peak demands and droughts. Reserve capacity is expensive to construct and is operated infrequently. The use of system storage of treated water to meet hourly variations in supply and demand is cost-effective and conventional practice, however, to date, storage of sufficent volumes of treated water to meet seasonal and other long term variations in demand is prohibitively expensive.
In an effort to reduce facilities expansion costs, water resource engineers have become increasingly interested in the concept of storing large volumes of treated water in aquifers during months of the year when both water supply and facilities reserve capacity are available, to be recovered during times of peak demand. Recharge of aquifers through wells using untreated water is also receiving increased attention, particularly in water short areas. This concept of seasonal storage is called Aquifer Storage Recovery, or ASR. As an alternative to conventional expansion of water supply, treatment and distribution facilities, it is quite cost effective in areas where it is technically feasible. Generally the same wells are used for both recharge and recovery, and no retreatment of the water is necessary other than disinfection. The recharging of aquifers can be accomplished by using existing wells or by constructing new injection wells.
In addition to reduction in facilities expansion costs, other advantages favor ASR technology. In many coastal areas, low water levels in aquifers may permit the intrusion of salt water which can result in the destruction of the fresh water supply. In such areas, recharging of these aquifers can insure that conditions are maintained to prevent salt water intrusion, while at the same time helping to meet seasonal peak demands.
Such storage and water resource techniques have proven extremely advantageous and cost-effective in communities where declining ground water levels have left wells non-productive. They are beneficial in areas where existing ground water supplies are threatened by salt water or other contaminant intrusion. Well recharging is also effective where substantial storage reserves of treated water are necessary to improve system reliability in the event of a catastrophic loss to a primary water supply or in communities where additional strategically located water reserves are required to insure that pressures throughout a water distribution system are adequate during times of peak demand. Other environmental, water conservation and water quality benefits also favor ASR technology.
Although there are obvious benefits to be obtained from recharging existing water supply wells or in constructing new aquifer storage recovery wells, in many areas, problems have been encountered with air being entrapped in the aquifer thereby decreasing the effectiveness of recharging operations. Such air entrapment is most frequently encountered in areas or localities wherein one or more of three conditions exist. These conditions are encountered where the recharge water supply must drop a substantial depth to the existing subsurface water level; where the rate of recharge flow is relatively low; and where the specific capacity of the wells is relatively high. The foregoing adverse conditions have resulted in the cascading of water through the recharge well pipe thereby entrapping quantities of air which flow outwardly into the well or aquifer. The trapped or entrained air can thus effectively plug or seal the aquifer resulting in substantially lower storage capacity.
Although there have been many flow controllers designed and developed for use in the oil and gas industry, such controllers have not been designed nor are they suitable for use in controlling cascading in recharge, injection or aquifer storage recovery wells. One alternative which has been used for the elimination of the problems of air entrapment involves the use of multiple small injection tubes to supply the water to the aquifer. Such an alternative is only possible in wells having large well pipe diameters. It is therefore costly and is not generally suitable for retrofitting existing wells.